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Magnetic Fields on FIRE: Comparing B-fields in the multiphase ISM and CGM of Simulated L* Galaxies to Observations

Presentation #241.15 in the session Evolution of Galaxies — iPoster Session.

Published onJun 29, 2022
Magnetic Fields on FIRE: Comparing B-fields in the multiphase ISM and CGM of Simulated L* Galaxies to Observations

Simulations of galaxy formation have recently included the physics of magnetic fields and cosmic rays (CRs); however, significant uncertainties remain. To this end, we analyze the magnetic fields in a set of high-resolution, magneto-hydrodynamic, cosmological simulations of L* galaxies from the FIRE-2 project. We compare mock observables of magnetic field tracers for simulations with and without CRs to relevant observations: Zeeman splitting and rotation/dispersion measures (RM/DM). We find reasonable agreement between simulations and observations of both neutral and ionised ISM. We find that while simulations with CRs show weaker B-fields on average, this primarily owes to their being less massive and dense, moving along the same scaling relations, as opposed to CRs directly modifying magnetic amplification. Our results indicate that in the low density limit (nH < 300 cm -3 ) |B| follows a non-zero power-law scaling with density in agreement with existing data, contrary to some stochastic models fit to the observations. We also generate synthetic rotation measure (RM) profiles for face-on projections of the simulated galaxies and compare to observational constraints in the CGM. While consistent with present upper limits, improved data are needed to detect the predicted CGM RMs at 10-200 kpc. Finally, we comment on the validity and implications of equipartition estimates of |B| in the disk and halos of L* galaxies inferred from synchrotron intensity and virial temperatures.

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